1. Field
Apparatuses and methods consistent with exemplary embodiments relate to a tomography apparatus and a method of reconstructing a tomography image by using the tomography apparatus.
2. Description of the Related Art
Medical imaging apparatuses are used to obtain an image of an internal structure of an object. Medical image apparatuses that are non-invasive testing apparatuses capture images and provide a processed image to a user including processed structural details, internal tissues, and the flow of fluids in a human body. The user, who is, for example, a medical doctor, may diagnose a health state and a disease of a patient by using a medical image output from a medical image processing apparatus.
A computed tomography (CT) apparatus is a typical apparatus among apparatuses for capturing an image of an object by projecting X-rays to a patient.
Among medical image processing apparatuses, the CT apparatus may provide a cross-sectional image of an object that may show an internal structure (e.g., organs such as kidneys and lungs) of the object without overlapping elements in the internal structure, compared to a general X-ray apparatus. Therefore, the tomography apparatus is widely used for accurate diagnosis of diseases. Hereinafter, a medical image obtained by the apparatus is referred to as a tomography image.
To obtain a tomography image, a tomography scan is performed on the object by using a tomography apparatus, and thus raw data is obtained. Then, the tomography image is reconstructed by using the obtained raw data. The raw data may be projection data, which is obtained by projecting X-rays to the object, or a sinogram that is a group of pieces of the projection data.
For example, to obtain a tomography image, the tomography image has to be reconstructed by using a sinogram that is obtained through a tomography scan. The reconstruction of the tomography image will be described in detail with reference to FIGS. 1A and 1B.
FIGS. 1A and 1B are diagrams for describing a CT scan and reconstruction operations.
FIG. 1A is a diagram for describing a CT scan of a tomography apparatus that performs a CT scan while rotating around an object 25, and obtains raw data corresponding to the object 25. FIG. 1B is a diagram for describing a sinogram obtained by the CT scan and a reconstructed CT image.
The tomography apparatus generates and projects X-rays to the object 25, and detects X-rays passing through the object 25 by using an X-ray detector. The X-ray detector generates raw data that corresponds to the detected X-rays.
Referring to FIG. 1A, an X-ray generator 20 included in the tomography apparatus projects X-rays to the object 25. During the CT scan that is performed by the tomography apparatus, the X-ray generator 20 rotates around the object 25 and obtains first to third raw data 30, 31, and 32 according to a rotation angle. The first, second and third raw data 30, 31, and 32 are obtained by detecting X-rays that are applied to the object 25 at a position P1, a position P2, and a position P3, respectively. The raw data may be projection data.
To generate one cross-sectional CT image, the X-ray generator 20 has to perform the CT scan while rotating at least 180°.
Referring to FIG. 1B, a sinogram 40 is obtained by combining the projection data 30, 31, and 32 that are obtained by moving the X-ray generator 20 at a predetermined angular interval, as described with reference to FIG. 1A. The sinogram 40 is obtained by the CT scan that is performed as the X-ray generator 20 rotates during one cycle. The sinogram 40, which corresponds to one cyclic rotation, may be used to generate one cross-sectional CT image. According to specifications of a CT system, one cyclic rotation may be about more than a half turn or one turn.
A CT image 50 is reconstructed by performing a filtered back-projection on the sinogram 40, and the sinogram 40 is reconstructed by performing a forward-projection on the CT image 50.
The reconstructed CT image 50 may include various types of artifacts. The artifacts in the CT image 50 may decrease the quality of the tomography image 50, and thus hinder the ability of the user, such as a medical doctor, to accurately read the CT image 50 and diagnose diseases.
FIG. 2 is a diagram for describing motion artifacts in a reconstructed CT image 200. FIG. 2 illustrates the CT image 200 that is obtained by using a full reconstruction method in which an image is reconstructed by using raw data that is obtained by rotating around an object 210 by 360° or more.
Referring to FIG. 2, when motion artifacts are generated in the reconstructed CT image 200, an outermost edge 220 of the object 210 is unclear and overlapping due to the motion artifacts. Also, an inner edge 230 of the reconstructed CT image 200 is blurred due to motions of the object 210.
As described above, motion artifacts and blur artifacts in a CT image may decrease the quality of the CT image, and thus hinder the ability of the user, such as a medical doctor, to accurately read the CT image and diagnose diseases. Therefore, there is a demand to reconstruct a CT image with minimum artifacts.